Thermophone



| DE FOREST THERMOPHONE Filed March 13, 1920 2 Sheets-Sheet l INVENTOR Q NW Feb. 17," 1'925. 1,526,778

L. DE FOREST THERMOPHONE Filed March 13, 1920 2 Sheets-Sheet 2 INVENTOR Patented Feb. 17, 1925.

UNITED sures PATENT oFFlcs LEE DE FOREST, OF NEW YORK, N. Y., ASSIGNQR, BY MESNE ASSIGNMENTS, TO DE FOREST PHO'NOIILM CORPORATION, OF JERSEY CITY, NEW JERSEY, A CORPORA- TION OF DELAWARE.

'rnnnmornonn.

Application 'filed March 18, 1920. Serial No. 365,605.

To all whom it may concern:

Be it known that I, LE on Fonns'r, a citizen of the United States, residing at New York, county of New .York, State of New York, have made a certain new and useful Invention .in Thermophones, of which the following is a specification.

This invention relates to thermo-phones.

The object of the invention is to provide a thermo-phone which is simple in construction, eificient'in operation, and which permits the use of the same for the reproduction of sounds in an exceedingly loud tone.

-Other objects of the invention will appear morefully hereinafter.

The invention consists substantially in the construction, combination, location and relative arrangement of parts, all as will be more fully hereinafter set forth, as shown by the accompanying drawings, and finally pointed out in the appended claims.

Referring to the drawings,

'Fig. 1 is a view in plan, largely diagramnratic, showing a thermo-phone arrange- 26 ment embodying my invention.

' Fig. 2 is a sectional view taken on the line 2-2, Fig. 1, looking in the direction oft-he arrows.

Fig. 3 is a top plan View of a slightly modified construction of thermo-phone embodying my invention. Fig. 4 is a sectional view taken on the line 4, 4, Fig. 3, looking in the direction of the arrows.

Fig. 5 is a diagrammatic view showing a still further modified arrangement embodying my invention.

Fig. 6 is a sectional view showing the application of a thermo-phone of my invention applied to a parabolic reflector.

Fig. 7 is a sectional view showing a still further modified form of thermo-phone embodying my invention.

Fig. 8 is a sectional view showing th form of thermo-phone illustrated in Fig. 7 used in connection with a parabolic reflector.

Fig. 9 is a sectional view showing a portion of the conductor in its mode of application.

The same part is designated by the same reference numeral wherever it appears throughout the several views.

My invention primarily relates to improvements in thermo-phones as applied to the problem of loud speakers. In other 5 words, to use a very fine wire or ribbon conductor, which conductor is heated by voice or sound controlled electric currents,

said conductor expanding and contracting thermo electrically with each and every fluctuation of the sound current, and thereby producing corresponding compression and rarification of the air surrounding or incontact with said conductor.

It has long been known to the art that a very fine platinum wire if enclosed in a small air space and made to conduct Voice electric currents will by its expansion and contraction, due to heat variations, produce sound waves in the small enclosed bodyof air surrounding the fine conductor. These sound waves are then communicated to the ear through a very small orifice in the wall of the small container within which is located the fine conductor, but if the line conductor is thus enclosed in a small vessel its "changes in volume resulting from changes in temperature cannot suiiiciently efi'ect compression waves in the surrounding air to produce broadly audible sound, therefore greatly limiting the use to which thermo-phones heretofore have been put. In other words, heretofore it has been very essential that the fine electric conductor be located in a very small air chamber in order 35 to produce the described thermo-phone effect; It will be apparent therefore that thermo-phones heretofore, due to the small volume of air affected as hereinbefore described, by the heat variation of the fine g conductor, have been contained in vessels of limited size which could be inserted directly into the outer passages of the ear obviously rendering it impossible to use the thermo-phone principle to produce loud 5 sounds which can be heard at a distance from the thermo-phone. It is the special object of my present invention to produce such loud sounds from a fine electric conductor heated by electric sound waves and thus secure all of reproduction without lag, distortion or harmonic vibrations due to the natural period of the vibrating member or d1aphragm, which advantages have always heretofore prevented perfect reproduction of sound from electric currents where a large volume of sound is required.

1n carryin out my invention I use preferably a circu ar disk of insulated material similar to the well known phonograph disk, and on the same I cut a fine narrow spiral groove similar to the track in the phono-.

graph disk, but deeper than thatordinarily In the employed in phonograph records. bottom of this long spiral groove illustrated at 2 in Fig. 1, the disk being illustrated at 1, I deposit in any suitable mannerffor example, electrolytically, a-fine conducting ribbon of any suitable materiahfor example, copper, silver, platinum, or the'like, which ribbon 3 or filamentlies preferably only at the bottom of the spiral groove as illustrated in Fig. 2. If the total resistance of this fine spiral is too great I make a number of con nections to various points thereof so that various sections of the spiral are connected in series or parallel, or series parallel, arrangement, as shown in Fig.1, so that the total impedance of the fine conductor would be equivalent to that of the secondary of a transformer, where a transformer --is employed, or source of. electrical sound curr ents \VlllCll are to be reproduced. Such an arrangement is shown in Figs. 1 and 2 where the source of sound controlled currents are supplied to a secondary winding 4 of a transformer, preferably of audio frequency type, which transformer is connected at its terminals to the various points of the spiral as desired and as above described. The source of sound controlled current may be any suitable source, and while I have shown the same in Fig. 1 to constitute the plate filament circuit of an audion amplifier 5, I do notdesire to be limited or restricted in this respect. In the form shown, however, the primary coil 6 of the audio frequency trans former is connected between the plate and filament and included in the circuit with the usual B-battery 7. Further, the audion amplifier may be the lastaudion of a series of amplifiers connected in any well known arrangement, for example, as shown in my copending application, Serial No. 7 7 5,529, filed June 24, 1913. I have found that a great increase in the accumulative action of the sound changes in the various portions on the groove on such a disk 1 as illustrated in Figs. 1 and 2 is obtained by mountin directly over this disk and separated y a slight distance-therefrom. for example, one sixteenth of an inch, another disk 15 having a flat surface opposing the grooved surface of the first disk 1 as illustrated in Fig. 2. By this arrangement the integrated air displacement from all the grooves is brought out at all portions of the crevice between the outer peripheries of the two disks 1 and. 15 which results in a very c'onsiderable displacement of the surrounding and exterior air. Such an arrangement is Well adapted to long sound waves, but where high frequencies are-to be reproduced, say of three thousand per second, where thewave-length involved is only two inches or three inches.

- interference may be produced. between the sound impulses originated from the inner grooves of the disk and those fromthe outer grooves. To avoid possible interference between the sound waves of the respective portions of the disk I cut the upper disk 15 into a plurality of concentric sect1'ons'20, 21, and 22, as shown best in Figs. 3 and 4, with a concentric opening 23 between the'respecvtive sections whereby the maximum distance which a sound wave must travel'from any portion of a groove to the crevice or opening 23 into the outer air does not greatly exceed one inch. I have also found that the thermophone effect is greatly enhanced when the fine ribbon or conductor 3 is fluted or corrugated rather than'la'id fiatQinthe groove, consequently I prefer'to cut my groove in the disk in sinusoidal form as shown best in Fig. 2) and deposit upon this sinusoidal track or groovethe thin metallic conductor 3. In order to obtain an amplified directive effect of the .sound emerging from the periphery or crevice of the above described arrangements, I cut the groove in a conical or parabolic formed disk as shown at 30,'F1g. 6,

and mount this grooved disk in the apex of a conical or parabolic reflector 31." With such an arrangement I am able to secure a large volume of sound thrown out in the direction of the axis of the reflector, which sound is a practically perfect reproduction of the original sound before this has been transformed into electric currents, amplified.

and again retransformed into sound waves by means of the thermo-phone arrangement hereinbefore described. As a variation ofthe above described spiral arrangement, and as a modification embodying my invention. I may use a large number of radial grooves each containing a conductor ribbon 3 spreading out spoke-like from a common circular conductor 32 and terminating similarly on an outer circular conductor 33. as shown, for example, in Fig. 5. If the combined resistance on all such fine radial conductors I, when connected in parallel is too small I cut my inner and outer circular conductors 51-2 and 33 respectively, as illustrated, into sections and connect these sections in series arrangement as shown in Fig. 5. It will be apparent, however, that any suitable arrangement of series, parallel, or series par- 3 are laid at the bottom of the narrow allel, grouping of the various portions of the fine radial conductors can be made. In 5, as in the other figures, the fine conductors grooves in a disk so as to obtain the effect of enclosing the small body of air which is to be directly acted upon by the heating-and cooling of the conductor. This will be readily apparent to those skilled in the art even though Fig. 5 is largely a diagrammatic illustration of the principle involved I I wish it to be understood that I do'not desire to be limited or restricted to any particular style or form of conducting material, for example, it is not necessary that the conductor be on a flat disk located in the groove thereof as hereinbefore described, as the same ma readily be located in grooves having the orm of a winding on a cyhndrical member as illustrated in Fi 7. In this arrangement I provide a cylinder 40 around which the conducting ribbon 41.is wound, and the cylinder with its windin is enclosed in a casing 42 formed prefera ly in two arts with the crevice or opening 43 prefera ly in the form shown at the a roximate center of the cylinder. It will lie apparent that the casing 42 being slightly larger than the cylinder forms a more or lessconfined space between the casing and the cylinder to contain the air to be e ected bv the thermo expansion and contraction of the conductor 41, which efiect is transmitted to the surrounding air through the crevice 43. In this form of m invention it will be apparent that it won d not be necessary to locate the conducting ribbon 41 in the grooves in the manner illustrated, but may, if desired, be wound on the smooth exterior surface of the. cylinder. Also in this form of my invention I find it preferable not'to wind the ribbon closely at the central portion thereof directly under the openin or crevice 43. In Fig. 8 I have illustrated ow the type of thermo-phone reproducers illustrated in Fig. 7 may be employed located in the axis of a parabolic reflector in the same manner as the disk type of thermo-phone reproducel' was used in connection with Fig. 6. Likewise many other modifications and changes in detail will readily occur to those skilled inthe art without departing from prisin said depressions in accordance with thermoelectric stresses set up in said conductor.

2. A thermic source of sound waves com.-

a long conductor of electricity spiral y shaped, means provided vwith depressions for confining said conductor and with grooved depressions confining means for converting. thermoelectric changes in said conductor into audible repro uctions.

3. A source of sound waves comprisin an elongated wave-shaped conductor 0 electricity supported and arranged to be thermo-electrically influenced by and in accordance with thermo-electric stresses set up in said conductor, and means for audibly reproducing said stresses.

4, Means for eflecting thermo-electric stresses and f or"converting and audibly reproducing said stresses, comprising a long flat conductor of electricity, a body provided with a continuous groovewithin which said conductor is'located, and means for initiating said stresses. I

5. Meansfor efi'ecting thermo-electric stresses and for. converting and audibly reproducing said stresses, comprising a body provided with a continuous grooved seat of sinusoidal cross section, and athin conductor seated within said groove, and means for effecting sald stresses in and about said conductor.

6. Means for audibly reproducing thermoelectric'chan es set up about an electric conductor, whic comprises means for initiatng said changes, means for converting said initiated changes into audibility including a support prov1 ed with a continuous ove, a thin electric conductor supported in said groove, and means for increasing cumulative action of said audibility changes.

7. Means for translating into audibility thermo-electric changes comprising means for initiating said changes, means for converting'said changes into audibility including a grooved support, a long, thin electric conduct-or disposed within the bottom of said groove, and means for directing cumulative audibility changes.

8. A thermic source of sound waves comprising spaced elements and a body provided with a continuous groove, a continuous conductorof electricity located therein. in proximity of said spaced elements for increasing and separating the accumulative action of sound changes, and means for supplying current to said conductor varied in strength in accordance with the sound disturbances.

9. A thermic source of sound waves comprising spaced elements and a body provided with a continuous spiral groove, a continuous conductor of electricity located therein, and means for variably heating said conductor in accordance. with the sounds to be roduced. a

10. thermic source of sound waves comprising spaced elements and a body provided with a continuous spiral groove, a continuous conductor of electricity located therein,

and means for supplying current to said. conductor varied in strength in accordance with the sounds to be produced.

11. A thermic source of sound waves comprising spaced elements and a body provided with a continuous groove, a continuous conductor of electricity located at the bottom thereof, and means for variably heating said conductor in accordance with the sound to be produced.

12. A thermic source of sound waves comprising spaced elements and a body provided with a continuous groove, a continuous conductor ofelectricity located at the bottom thereof, and means for supplying current to said conductor varied in strength in accordance with the sounds to be produced.

13. A source of sound waves comprising a. continuous track or groove of irregular contour in longitudinal cross section, and a continuous electrical conductor of similar contour located therein.

14. A source of sound waves comprising a continuous track or groove of wave. shaped contour in longitudinal cross section, and a continuous electrical conductor of similar contour located therein.

,l5. A source of sound waves comprising a body having a continuous shaped groove and a long continuous electrical conductor therein, a second body disposed adjacent to said first body with its surface thereof parallel'to the surface of said first body and separated therefrom to provide an air space therebetween.

1 6. Asouroe of sound waves comprising a body provided with an irregular depression and a spirally wound electrical conductor contained therein, a second body with the surface thereof parallel to the surface of said first body, and separated therefrom toprovide an air space therebetween.

17. A source of sound waves comprising a body having a spiral depression and a long continuous electrical conductor therein, a'second body with the surface thereof parallel to the surface of said first body and separated therefrom to provide an air space therebetween, and means for heating said conductor in accordancenwith the sounds to be produced. -.1 I

18. A source of sound waves comprising a body having a spiral depression and a long continuous electrical conductor therein, a second body with the surface thereof parallel to the surface of said first body and separated therefrom to provide an air space therebetween, and means for supplying current to said conductor varied in strength in accordance with the sounds to be produced.

19. The combination with a circular disk Q having a spiral groove cut therein, an elec- [trical conductor located in said groove, a

member with one surface positioned par- 'allel to the surface of said disk, but spaced therefrom to form an air space therebetween, and means for supplying current to said conductor varied in strength in accordance with the sounds to be produced.

21. The combination with a circular disk, of a spiral groove cut therein, an electrical conductor located in said groove, a plurality of ring members each provided with under surfaces parallel to said disk, but

spaced apart therefrom to form an air space therebetween, said ring members being radially spaced apart from each other, substantially as and for. the purpose set forth.

22. The combination with a circular disk, of a spiral groove cut therein, an electrical conductor located in said groove, a plurality of ring members each provided with under surfaces parallel to said disk, but spaced apart therefrom to form an air space therebetween, said ring members being radially spaced apart from each other, and means for variably heating said conductor in accordance with the sounds to be produced.

In testimony whereof I have hereunto set my hand on this 8th day of March A. D.

. LEE :on FOREST. 

